Atomic layer deposition (ALD), originally known as atomic layer epitaxy (ALE), is an advanced form of vapor deposition. ALD processes are based on sequential, self-saturated surface reactions. Examples of these processes are described in detail in U.S. Pat. Nos. 4,058,430 and 5,711,811. The described deposition processes benefit from the usage of inert carrier and purging gases, which make the system fast. Due to the self-saturating nature of the process, ALD enables almost perfectly conformal deposition of films on an atomic level and precise thickness control.
Low resistivity metallic films, such as metal carbide, metal nitride and metal carbonitride thin films are important materials for metallization applications in the semiconductor industry. These applications include, for example, gate metals, copper diffusion barriers for copper interconnects, metal electrodes for capacitors, and resistors. These applications typically call not only for low resistivity, but also for precise control of film thicknesses and/or excellent conformality in high aspect ratio structures. As a result, a thermal ALD process would be advantageous. In particular, in the case of tantalum-containing thin films, it has been difficult to deposit a thin film that has both low resistivity and a sufficiently low process temperature without supplying external energy, such as in plasma assisted deposition processes.